the way to do this is to explain to the audience that the terror filled catacombs and corridors beneath tristram are filled with the horrors of hell.
the fright of the people, plague, war, famine, are nothing compared to the minions of terror, or the champions of the prime evils.
lazarus would have a major role, as would griswold, deckard, wirt and farnham, considering they saw the butcher first hand. the knights of leoric would have to be mentioned, and how they were cursed to follow in King Leoric's corruption, his madness caused by diablo's attempt to possess the weakened king.
books and tomes would further explain the tale of the high heavens fighting the burning hells. the tale of the lesser evils banishing the prime evils to the mortal world of Sanctuary, resting upon the back of the dragon Trang'oul. how the awesome powers of this world, wielded by bright heroes, can be twisted and made to serve evil. How under the guise of men, angels and demons fight an everlasting battle.
and then, as we've seen the world turn for the worse, we get a glimpse of our warrior of light fighting the shadow. then, we see the full extent of diablos powers wreaked upon the denizens of hell, transforming them and binding the damned to his dark will.
we see those beasts unleashed against our hero beneath tristram. we see his fear, we see the anticipation building, the heat intensify, the light fade.
then we reach the chamber of lazarus and the boy prince, albrecht, surrounded by a foul cabal of demons and succubi.
and through the portal, awaits diablo and his most potent forces yet.
its about sending a message. until we have somebody who knows what D1-D2 are really, truly, essentially about, this movie will by the gods, never be made by unworthy humans.
"few are worthy to stand in its presence. fewer can still comprehend its true purpose"